Control system



29, 3 c. s. RUNNEh 2,019,320

CONTROL SYSTEM Filed Jl'me 21, 1954 Fig. I. I?

Fig. 2.

Inventor Claude C. Runnr I x fii l jtirn ey Patented Oct. 29, 1935 -U NlTED STATES PATENT OFFICE CONTROL SYSTEM New York Application June 21,1934, Serial No. 731,658

5 Claims.

This invention relates to control systems, more particularly to control systems for electromagnets and the like, and it has for an object the provision of a simple, reliable and improved system Q of this character..

' More specifically the invention relates to electromagnets utilized to hold articles in position while certain operations are performed. For exthe connections of the magnet coil to a source,

t estimating the amount ofv time required for demagnetization and then opening the reverse connections. If the estimate was erroneous, repetition of the entire sequence of operation was necessary, thus causing considerable delay and a cor- 25 responding decrease in the output. Accordingly, a further object of the invention is the provision of means for eliminating all guess work and judgment and positively effecting demagnetization of the electromagnet in the minimum possible time. 30 In carrying the invention into effect in one form thereof, means are provided for reversing the connections of the magnet coil to the source, and time element means are provided for interrupting t'nese'reverse connections a predetermined interval 0! time after their establishment.

For a better and more complete understanding of the invention, reference should now be made to the following specification and to the accompanying drawing in which Fig. 1 is a simple diagrammatical illustration of an embodiment of the invention. and Fig. 2 is a simple diagrammatical illustration 01 a grinding machine and magnetic chuck to which the invention is applicable.

Referring now to the drawing, a stone: II! is secured to and rotated by means of a spindle II, which in turnis connected. to and rotated by means of an electric motor I2. The article to be ground or polished by the stone is held securely in place by means of a magnetic chuck I3. which in turn is mounted in a reciprocating table I4.

Only the core portion of the chuck is shown in Fig. 2. The chuck, however, is provided with a magnet coil I5, by means 0 which the core is energized. 'The force required to maintain the work object securely in position during milling or grinding operation, is otten avery considerable amount, and for this reason the magnetizing coil I5 has many turns of fine wire, and the coil is so designed thatthe ampere turns are sufficient to exert the maximum magnetizing force required. 5

Due tothe large number of ampere turns required a very considerable amount of energy is stored in the magnetic field Furthermore, the work which is held by the magnet acts asakeeper for the magnetic core strugture. I magnet coil I5 is merely deenrgized when the grinding or milling operation is completed, the residual magnetism of the magnetic structure will persist in suflicient strength to prevent the removal of the work for several hours.

In order to provide rapid demagnetization ot the electromagnet and prompt removal ofthe work iromthe chuck in order to provide for repetition of the grinding or milling operation on a succeeding piece of work, the control system shown diagrammatically in Fig. l is provided.

As illustrated in Fig. 1, the coil I5 of the electromagnet is arranged to be connected to a suitable source of direct current represented by the supply lines I6. Suitable switching means illus- 5 trated as an electromagnetically operated contactor H are provided for eflecting the connection of the coil I5 to the 'source. The contactor I1 is provided with a pair of movable contacts, which when moved into engagement with the stationary contacts 20, 2|, connect the coil I5 of the electromagnet to the source for the purpose of energizing the magnet so as to hold the work piece securely. Also the contactor I1 is provided with a. pair of stationary contacts 22 and 23, which, when engaged by the movable contacts, reverse the connections of the coil I5 of the electromagnet to the source to provide for demagnetization of the electromagne't and release of the work piece,

In order to prevent the disconnection of the coil 40 I5 from the source prior to complete demagnetization or subsequent thereto, a time element device 24 is provided having a pair of contacts 24a included in the reverse connections. Although any suitable type of time element device may be used, it is preferred to utilize a device having a magnetic core structure 24s provided with a copper jacket 24:1. The time element device 24 is provided with an adjustable tension spring 25 for adjusting the time delay drop-out action or the device 24 to 5 the exact predetermined time interval required to effect disconnection of the coil I5 from the source I6 when the magnetization of the electromagnet is substantially zero.

Control means, illustrated as a push button Thus, it the 10' device 24 device it closes its contact 24..

switching device II are provided for controlling the operation of the contactor l'l in establishing and reversing the connections between the coil I! of the electromagnet and the source II. A discharge resistance device 21 is connected across the magnet coil II. This resistance may be of any suitable type.

With the above understanding oi the elements and theirorganization in the completed control system, the operation oi the system itseli' will readily be understood from the following detailed description. Assuming a piece of work to be placed on the core surfaces I! of the electromagnetic chuck, the electromagnet is energized by depressing the start button 28 to bridge its cooperating stationary contacts. This completes an energizing circuit for the operating coil 01' the contactor l1, which circuit is readily traced from the upper supply line It through the coil 01' the contactor, through conductor Ill, stationary contacts bridged by the button 28, normally closed contacts of the stop push button it to the lower side of the supply source It. contactor II in responding to energlzation, moves its movable contacts into engagement with upper stationary contacts 20 and 2|, thereby connecting the coil I! of the electromagnet directly to the supply source it. Contactor ll in closingv also operates its auxiliary movable contact member l1. into engagement with cooperating stationary contact "a thereby to complete a holding circuit for the operating coil 01' 'thecontactor independent 01 the start button 2., which may now be released.

J The engagement oi the lower main movable contact member of the contactor ll with the upper stationary contact 2| completes an energizing circuit for the operating coil of the time delay the upper supply line It through conductor 32, coil of time delay device 24, lower main contact oi contactor l1, contact 2i and conductor 33 to the lower side of the supply'source It. In response to the energization of its coil, time delay The closing oi this contact, however, has no eflect at this .time since the movable contact member 24. is connected to the lower stationary contact 22 of the contactor II, which at this time is not engaged by the movable contact of the contactor.

When the milling or grinding operation 01' the work is completed and it is desired to demagnetize the chuck and remove the work to make way for a new piece, the stop button II is depressed to interrupt the energizing circuit for the operats coil of the contactor l1. As a result of deenergization, contactor i'l allows its movable contacts to descend out of engagement with stationary contacts II and 'II and into engagement with stationary contacts 22 and 23. This obviously reverses the connection of the electromagnet-coil II to the supply source ll, since the'lefthand terminal of this coil; which was previously connected to the upper supply line I. is now con which circuit is readily traced from duration of which is determined by the setting of the adjusting spring 25, and which is just suflicient to allow the magnetism of the electromagnets II. II to decay to zero, the time element device 24 opens its contacts 24., thereby to interrupt the reverse connection oi the magnet coil I! to the source It, thus deenergizing the coil when the electromagnet is deenergized, thus al-. lowing the removal of the work piece and replacement by a new piece. l

While in accordance with the provisions of the patent statutes, this invention is described as embodied in concrete form, it will be understood that the elements and connections shown and described are 'merely illustrative and that the invention is not limited thereto, since alterations and modifications will readily suggest them selves to persons skilled in the art without departing from the true spirit of this invention, or from the scope oi the annexed claims. '1 What I claim as new and'desire to secure by Letters Patent 01 the United States is: a

1. A control system for an electromagnet comprising a switching device for connecting the coil oi said magnnet to a supply source and for subsequently establishing reverse connections, between said coil and said source to-demagnetize, said magnet, a separate time element; device and contacts in said reverse connections" controlled by said time element device, and connections controlled by said switching device for energizing said time element device to closesaid contacts priorto establishment of said reverse connections and for deenergizing said time element device upon establishment at said reverse connections 3 thereby to open said contacts a predetermined interval of time after establishment of said reverse connections.

2. A control system for electromagnets comprising an electromagnetic contactor for con- 4' ing of said contacts a predetermined interval of time atter establishment of said reverse connections. I

3. A control system for an electromagnet comprising a contactor for connecting the coil of said magnet to a source of supply and for subsequently establishing reverse connections between said coil and said source to demagnetise said magnet, a time element device having contacts in said reverse connections and an operating coil, connections between said operating coil and said contactor providing energimtion 01 said coil to close said contacts when said magnet coil is first connected to said source and short-circuiting said operating coil upon establishment 0! said reverse connections thereby to eirect opening of. said contacts a predetermined interval of time after establishment of said reverse connections. 7

4. A control system for the coil oi an electromagnet comprising a time element device having an operating coil and a pair 01' normally open til source independently 01 said normally open contacts and for connecting said operating coil to said source to close said normally open contacts,

said contactor also being provided with contacts for establishing reverse connections for said magnet coil thereby to demagnetize said magnet and for short-circuiting said operating coil thereby to open said normally open contacts and interrupt said reverse connections a predetermined interval of time after establishment.

5. A control system for an electromagnet comprising a contactor for connecting the magnet coil to a source of supply and for subsequently establishing reverse connections between said coil and said source to demagnetize said magnet,

a time element device having normally open contacts in said reverse connections and provided with an operating coil, connections between'the operating coil of said time element device and the contacts 01' said contactor providing energize,- tion 0! said coil to close said normally open contacts when said magnet coil is first connected to said source and short-circuiting said operating coil upon establishment 01 said reverse connections thereby to effect opening or said reverse connections a predetermined interval of time after establishment, means for varying the duration 01' said time interval, an energizing circuit for said contactor, and manually operated switching means for controlling said circuit.

CLAUDE C; RUNNER. 

